The present invention relates to an anti-decubitus pneumatic mattress. More particularly, the present invention relates to an anti-decubitus pneumatic mattress that is adapted to replaceably overlay a conventional mattress of a bed and have a patient lie thereon and be moved in preselected ways so as to prevent the patient from having skin breakdowns, and which prevents the patient from falling off the bed when the patient is turning, and which further prevents the patient from bottoming out on a low side of the turning, while being suspended in a cushion of static air if power fails.